58 MISSOURI AGR. EXP. STA. RESEARCH BULLETIN 49 



sible to adjust the yields by a somewhat shortened method. If adjust- 

 ment of yield is effective in reducing plot variability in this sort of 

 test it can be accomplished with but little increase in labor. In each 

 of the tests reported in this paper a trial of the effectiveness of adjust- 

 ing yields by means of check plots was made, the criterion of accuracy 

 being in each case the variability of the yields of the replicate plots of 

 each variety. Since the number of replicate plots was only three 

 or four the average deviation was determined instead of the stand- 

 ard deviation. 



Method Used in Adjusting Yields. The method employed in ad- 

 justing yields may be described as follows: The average yield of all 

 check plots and the relative yield of each check plot in terms of this 

 average (that is, the quotient obtained by dividing the yield of the in- 

 dividual check plot by the average yield of all check plots) were de- 

 termined. The relative yield of each check plot, expressed in per- 

 centage of the mean check yield, is designated hereafter as the "plot 

 value" of that check plot. When the average yield of all check plots 

 is 25 bushels per acre, the plot value of a check plot yielding 30 bushels 

 per acre is 120 per cent in other words it is 20 per cent more pro- 

 ductive than the average. Now assuming gradual change in the pro- 

 ductivity of the soil between check plots, each test plot is assigned a 

 plot value by interpolation. The adjusted yield of each plot is then 

 determined by dividing the actual yield by the plot value. 



The short method for adjusting yields, referred to above, is 

 based on the fact that the varieties occur in the same order in each 

 series. Thus in the field diagrammed in figure 1, the following se- 

 quence of plots occurs in each of the four series : 



ck 1 17 33 49 65 81 ck 



Now if the average yield of the four check plots adjoining variety 

 1, and the average yield of the four check plots adjoining variety 81 

 are each given a plot value, corresponding plot values for the mean 

 yields of varieties 1, 17, 33, 49, 65, and 81 may be interpolated, and 

 the mean yields may be adjusted in one operation. The same method 

 may be used, of course, regardless of the number of replications. The 

 result will not be exactly the same as that of averaging the adjusted 

 yields determined individually, but will in most cases approximate it 

 closely, the slight difference being caused by the disproportion of yield 

 and plot value in the plots averaged. It is doubtful that either meth- 

 od is consistently more accurate than the other. 



When the check plot yield is used in the adjustment of the yields 

 of other plots it is of course essential that it should be a reliable de- 

 termination, not unduly affected by factors not affecting the neighbor- 



